The introduction of fresh air into the exhaust path of internal combustion engines has been shown to reduce levels of undesirable emissions in automotive vehicles. Consequently, air management systems AMS, or systems used to control how much, when and where air is introduced into vehicle exhaust, are commonly used in conventional emission control strategies. The reliability of these systems is encumbered by their complexity and by the harsh environments in which they necessarily must operate. AMS faults can result in unfavorable oxygen levels in vehicle emissions which can lead to catalytic converter damage or unacceptable vehicle emissions. As such, the detection of faults in these systems, such that they may be promptly treated, facilitates the goal of improving vehicle emissions.
Conventional systems that attempt to detect some AMS faults exist in the art. Commonly, they may use a single oxygen sensor to detect AMS faults, where the sensor should indicate an excess of oxygen in the exhaust when fresh air is being injected into the exhaust. Other conventional systems use off-board techniques to diagnose the integrity of AMS systems.
The single sensor systems use a sensor already available in the exhaust path for engine air-fuel ratio control. This sensor is commonly attached to the exhaust manifold of the engine, and thus cannot monitor air injection at points in the exhaust path after the sensor, for example in the catalytic converter. In dual bank engines, where the sensor is commonly located on one bank and air is injected in the other bank, AMS faults affecting the injection point on the bank cannot be detected. Additionally, if the single sensor fails, the air management system is left without on-board fault detection recourse.
The off-line techniques are subject to the shortcomings of inconvenience and the potential for substantial delay between the time the failure occurs and the time it is diagnosed. Without some indication of a failure, the driver will not likely submit the vehicle to off-line testing, unless some external motivation exists. Even with such a motivation, the period between the time of the failure and the time of the diagnosis of the failure through a routine test may be substantial.